The present invention relates to magnetoresistive elements having a differential effect and more particularly, a semiconductor magnetoresistance device provided with at least three terminals and making use of magnetoresistive effect.
A conventional semiconductor magnetoresistive element comprises, as shown in FIG. 1, a current-carrying magnetoresistive (magnetic field sensitive) portion 5 in the form of an oblong semiconductor plate or thin film and a pair of electrodes 1 and 2 provided at the opposite ends of the magnetosensitive portion, in which the resistance between the electrodes 1 and 2 of the element is changed by applying a magnetic field to the magnetosensitive portion 5. In order to increase the rate of change in the resistance or application of the magnetic field in the magnetroresistive element, metal electrode bars in ohmic contact with a semiconductor body constituting the magnetoresistive portion are usually used to short the Hall voltage. The electrode bar is called a shorting bar. The shorting bars are made of conducting material and are aligned between input and output electrodes 1 and 2 on the semiconductor body at right angles to the direction of current flow as indicated by 3 in FIG. 1. The shorting bars 3 segment the magnetosensitive portions to form small regions. A ratio l/w between a length l and a width w of the segmental region is reduced to obtain the maximum shorting effect for the Hall voltage. The segmental regions are electrically connected in series to complete a unitary element. As the ratio l/w is reduced, the resistance of the semiconductor element is increased in square proportion to a low applied magnetic field but in direct proportion to a high applied magnetic field, irrespective of the direction of the applied magnetic fields.
Another magnetoresistive element is also known using an InSb material containing acicular, low resistivity NiSb. The NiSb crystal acts as shorting bars, offering similar characteristics.
However, with the conventional magnetoresistive element having the electrodes only at the opposite ends, the resistance in the absence of the applied magnetic field varies with temperatures and hence, when placing the element into operation, it is necessary to compensate the variation in resistance due to temperatures by means of an external circuit. For example, two discrete elements are used in combination, in which these elements are connected in series to produce a differential output.
Accordingly, additional separate parts and interconnecting means therefor are required to compensate the temperature dependence of the resistance. In the application to devices such as a contactless micro-switch and a contactless potentiometer, these elements suffer not only the increased number of separate parts but also necessity of IC (integrated circuit) parts associated therewith, resulting in a bulky device. Without the compensation of the temperature dependence a strict restriction will be imposed on the application of the magnetoresistive element since the element is allowed to be operated only in a substantially constant ambient temperature.
An approach has been proposed as disclosed, for example, in Japanese Laid-open Patent Application No. 53-8180 laid open to public on Jan. 25, 1978 (Japanese Patent Application No. 51-82125 filed on July 10, 1976), in which two magnetoresistive elements are formed on a substrate in a unitary fashion and a magnetic field is applied to only one of the elements to produce a differential output. With this approach, if the magnetic field is applied to both the elements, respective elements equally change their resistances, and therefore, it results in no differential output. Thus, it is necessary to apply the magnetic field to only one of the elements to produce a differential output. In addition, a utilization device incorporating such unitary element inevitably becomes bulky.
As a countermeasure therefor, a three-terminal element as shown in FIG. 2 is known, in which a magnetic field may be applied to an overall element. As diagrammatically shown in FIG. 2, two thin film magnetosensitive portions are disposed on one surface of a substrate 8 in such a manner that they are geometrically perpendicular to each other. A power supply E is connected between electrodes 1 and 2 of the element. By applying a magnetic field parallel to the substrate a differential output V.sub.out with small temperature dependence can be developed at an intermediate electrode 4. This arrangement, however, is inherent and specified to a ferromagnetic magnetoresistive element constituted by a magnetosensitive portion made of a ferromagnetic material and hence cannot be applied to semiconductor magnetoresistive elements.
The variation in the resistance of semiconductor magnetoresistive element due to temperatures has long been taken little account of by the conventional technique because of its inherent dependency upon the characteristics of the semiconductor material used for the magnetosensitive portion.